In recent years, microring resonators (“resonators”) have increasingly been employed as an essential component in optical networks and other nanophotonic systems that are integrated with electronic devices. A resonator can ideally be configured with a resonance frequency (or wavelength) substantially matching a particular frequency of light. When the resonator is positioned adjacent to a waveguide within the evanescent field of light propagating along the waveguide, the resonator evanescently couples the light from the waveguide.
A resonator's dimensions directly affect the resonator's resonance frequency, which is particularly important because in typical WDM systems the frequencies may be separated by fractions of a nanometer. However, even with today's microscale fabrication technology, fabricating resonators with the dimensional precision needed to ensure that the resonator's resonance frequency matches a particular frequency of light can be difficult. This problem arises because a resonance frequency of a resonator is inversely related to the resonator's size.
In addition to inaccuracies encountered during fabrication of resonators, environmental conditions can change the resonance frequency of a resonator. For example, a temperature change in the resonator shifts the effective refractive index and may change the size of the resonator resulting in deviations from a desired resonance frequency. This is problematic in integrated CMOS-nanophotonic systems where the power dissipation and temperature of adjacent circuitry can vary considerably over time.
Engineers and physicists continue to seek systems and methods for tuning resonators to compensate for resonance frequency deviations due to fluctuations in environmental conditions and fabrication inaccuracies.